The present invention relates to a voltage controlled oscillator (VCO) having a wide-band oscillation frequency range. In particular, the invention relates to a VCO which suppresses influences of disturbance and noise.
The VCO is provided in a phase locked loop (PLL) circuit and used for a semiconductor device. An oscillation signal outputted from the PLL circuit is supplied to circuit blocks inside and outside the semiconductor device as a clock signal.
The VCO affects the accuracy and stability of oscillation characteristics of the oscillation signal of the PLL circuit. In the VCO, the characteristics of output oscillation frequency to an input voltage changes depending on of disparity of the manufacturing process of the semiconductor device, temperature of the operating environment, deflection of power supply voltage and the like. In recent years, semiconductor devices are required to have a wide-band oscillation frequency range. To satisfy this demand, oscillation frequency gain of the VCO to an input voltage needs to be increased in order to achieve a wide-band oscillation frequency range. However, there is a problem that when this oscillation frequency gain is increased, a change of the output oscillation frequency is increased due to a disturbance.